Can a three-wire flow meter be connected using a two-core cable?
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The dual-rotor flow meters installed in the project are all three-wire type, but the design drawings specify a two-wire system, with two-core cables being used. The manufacturer says that the shielding layer of the cable can be used as a third wire – is this acceptable? If possible, how should the wires be connected? If that’s not possible, are there any other options? This post was last edited by Goods delivered via wind paths on 2009-3-22 14:16.]
In this way, the cable loses its shielding effect and is likely to be subject to interference.
There’s really no other choice but to make do with it. When the conditions permit in the future, it is necessary to lay new cables for use. In a three-wire system, one wire is used to supply 24VDC power, another is connected to the positive terminal of the signal, and the third wire serves as the common com terminal; please refer to the manual for details.
The three-wire system requires an external 24Vdc power supply. The cabinet uses a 4-20mA four-wire connection, with the negative terminal of 24VDC connected to the negative terminal of the signal input.
It’s best not to connect it in this way, as it is prone to interference and can cause problems in future operations; instead, use a three-core twisted copper shielded cable.
It is best not to do this, as it can easily lead to a discrepancy between the cumulative values on the field gauge and those in the control room. If installed in this way, it is best to test these two values over a certain period of time.
I think this situation is also dangerous as well; in this case, it may no longer be possible to shield the cable, and interference is likely to occur
Another question is, will changing from a two-wire system to a three-wire system have an impact on the DCS configuration?